How can I detect a local player jumping and increase their jumpheight by 1 each time they do?

How can I detect a local player jumping and each time they jump increase their jump height by +1?

Use UserInputService.JumpRequest event. Make sure Humanoid.UseJumpPower is set to false.

local UserInputService = game:GetService("UserInputService")
local JumpHeight = 7.2 -- default is 7.2

UserInputService.JumpRequest:Connect(function()
	print("Player has jumped!")
	JumpHeight += 1 -- increases the height
end)